3 reportUnsolved, reportUnsolvedDeriv,
4 reportUnsolvedWantedEvVars, warnDefaulting,
5 unifyCtxt, typeExtraInfoMsg,
6 kindErrorTcS, misMatchErrorTcS, flattenForAllErrorTcS,
7 occursCheckErrorTcS, solverDepthErrorTcS
10 #include "HsVersions.h"
23 import HsExpr ( pprMatchContext )
29 import ListSetOps( equivClasses )
34 import StaticFlags( opt_PprStyle_Debug )
35 import Data.List( partition )
36 import Control.Monad( when, unless )
39 %************************************************************************
41 \section{Errors and contexts}
43 %************************************************************************
45 ToDo: for these error messages, should we note the location as coming
46 from the insts, or just whatever seems to be around in the monad just
50 reportUnsolved :: (CanonicalCts, Bag Implication) -> TcM ()
51 reportUnsolved (unsolved_flats, unsolved_implics)
55 = do { unsolved <- mapBagM zonkWanted unsolved
56 -- Zonk to un-flatten any flatten-skols
57 ; env0 <- tcInitTidyEnv
58 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfWanteds unsolved)
59 tidy_unsolved = tidyWanteds tidy_env unsolved
60 err_ctxt = CEC { cec_encl = []
62 , cec_tidy = tidy_env }
63 ; traceTc "reportUnsolved" (ppr unsolved)
64 ; reportTidyWanteds err_ctxt tidy_unsolved }
66 unsolved = mkWantedConstraints unsolved_flats unsolved_implics
69 reportUnsolvedWantedEvVars :: Bag WantedEvVar -> TcM ()
70 reportUnsolvedWantedEvVars wanteds
74 = do { wanteds <- mapBagM zonkWantedEvVar wanteds
75 ; env0 <- tcInitTidyEnv
76 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfWantedEvVars wanteds)
77 tidy_unsolved = tidyWantedEvVars tidy_env wanteds
78 err_ctxt = CEC { cec_encl = []
80 , cec_tidy = tidy_env }
81 ; groupErrs (reportFlat err_ctxt) (bagToList tidy_unsolved) }
83 reportUnsolvedDeriv :: [PredType] -> WantedLoc -> TcM ()
84 reportUnsolvedDeriv unsolved loc
89 do { unsolved <- zonkTcThetaType unsolved
90 ; env0 <- tcInitTidyEnv
91 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfTheta unsolved)
92 tidy_unsolved = map (tidyPred tidy_env) unsolved
93 err_ctxt = CEC { cec_encl = []
95 , cec_tidy = tidy_env }
96 ; reportFlat err_ctxt tidy_unsolved (ctLocOrigin loc) }
98 alt_fix = vcat [ptext (sLit "Alternatively, use a standalone 'deriving instance' declaration,"),
99 nest 2 $ ptext (sLit "so you can specify the instance context yourself")]
101 --------------------------------------------
102 -- Internal functions
103 --------------------------------------------
106 = CEC { cec_encl :: [Implication] -- Enclosing implications
108 , cec_tidy :: TidyEnv
109 , cec_extra :: SDoc -- Add this to each error message
112 reportTidyImplic :: ReportErrCtxt -> Implication -> TcM ()
113 reportTidyImplic ctxt implic
114 = reportTidyWanteds ctxt' (ic_wanted implic)
116 ctxt' = ctxt { cec_encl = implic : cec_encl ctxt }
118 reportTidyWanteds :: ReportErrCtxt -> WantedConstraints -> TcM ()
119 reportTidyWanteds ctxt unsolved
120 = do { let (flats, implics) = splitWanteds unsolved
121 (ambigs, non_ambigs) = partition is_ambiguous (bagToList flats)
122 (tv_eqs, others) = partition is_tv_eq non_ambigs
124 ; groupErrs (reportEqErrs ctxt) tv_eqs
125 ; when (null tv_eqs) $ groupErrs (reportFlat ctxt) others
126 ; when (null tv_eqs) $ mapBagM_ (reportTidyImplic ctxt) implics
128 -- Only report ambiguity if no other errors (at all) happened
129 -- See Note [Avoiding spurious errors] in TcSimplify
130 ; ifErrsM (return ()) $ reportAmbigErrs ctxt skols ambigs }
132 skols = foldr (unionVarSet . ic_skols) emptyVarSet (cec_encl ctxt)
134 -- Report equalities of form (a~ty) first. They are usually
135 -- skolem-equalities, and they cause confusing knock-on
136 -- effects in other errors; see test T4093b.
137 is_tv_eq c | EqPred ty1 ty2 <- wantedEvVarPred c
138 = tcIsTyVarTy ty1 || tcIsTyVarTy ty2
141 -- Treat it as "ambiguous" if
142 -- (a) it is a class constraint
143 -- (b) it constrains only type variables
144 -- (else we'd prefer to report it as "no instance for...")
145 -- (c) it mentions type variables that are not skolems
146 is_ambiguous d = isTyVarClassPred pred
147 && not (tyVarsOfPred pred `subVarSet` skols)
149 pred = wantedEvVarPred d
151 reportFlat :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
152 reportFlat ctxt flats origin
153 = do { unless (null dicts) $ reportDictErrs ctxt dicts origin
154 ; unless (null eqs) $ reportEqErrs ctxt eqs origin
155 ; unless (null ips) $ reportIPErrs ctxt ips origin
156 ; ASSERT( null others ) return () }
158 (dicts, non_dicts) = partition isClassPred flats
159 (eqs, non_eqs) = partition isEqPred non_dicts
160 (ips, others) = partition isIPPred non_eqs
162 --------------------------------------------
164 --------------------------------------------
166 groupErrs :: ([PredType] -> CtOrigin -> TcM ()) -- Deal with one group
167 -> [WantedEvVar] -- Unsolved wanteds
169 -- Group together insts with the same origin
170 -- We want to report them together in error messages
174 groupErrs report_err (wanted : wanteds)
175 = do { setCtLoc the_loc $
176 report_err the_vars (ctLocOrigin the_loc)
177 ; groupErrs report_err others }
179 the_loc = wantedEvVarLoc wanted
180 the_key = mk_key the_loc
181 the_vars = map wantedEvVarPred (wanted:friends)
182 (friends, others) = partition is_friend wanteds
183 is_friend friend = mk_key (wantedEvVarLoc friend) == the_key
185 mk_key :: WantedLoc -> (SrcSpan, String)
186 mk_key loc = (ctLocSpan loc, showSDoc (ppr (ctLocOrigin loc)))
187 -- It may seem crude to compare the error messages,
188 -- but it makes sure that we combine just what the user sees,
189 -- and it avoids need equality on InstLocs.
191 -- Add the "arising from..." part to a message about bunch of dicts
192 addArising :: CtOrigin -> SDoc -> SDoc
193 addArising orig msg = msg $$ nest 2 (pprArising orig)
195 pprWithArising :: [WantedEvVar] -> (WantedLoc, SDoc)
196 -- Print something like
197 -- (Eq a) arising from a use of x at y
198 -- (Show a) arising froma use of p at q
199 -- Also return a location for the erroe message
201 = panic "pprWithArising"
202 pprWithArising [WantedEvVar ev loc]
203 = (loc, pprEvVarTheta [ev] <+> pprArising (ctLocOrigin loc))
204 pprWithArising ev_vars
205 = (first_loc, vcat (map ppr_one ev_vars))
207 first_loc = wantedEvVarLoc (head ev_vars)
208 ppr_one (WantedEvVar v loc)
209 = parens (pprPred (evVarPred v)) <+> pprArisingAt loc
211 addErrorReport :: ReportErrCtxt -> SDoc -> TcM ()
212 addErrorReport ctxt msg = addErrTcM (cec_tidy ctxt, msg $$ cec_extra ctxt)
214 pprErrCtxtLoc :: ReportErrCtxt -> SDoc
216 = case map (ctLocOrigin . ic_loc) (cec_encl ctxt) of
217 [] -> ptext (sLit "the top level") -- Should not happen
218 (orig:origs) -> ppr_skol orig $$
219 vcat [ ptext (sLit "or") <+> ppr_skol orig | orig <- origs ]
221 ppr_skol (PatSkol dc _) = ptext (sLit "the data constructor") <+> quotes (ppr dc)
222 ppr_skol skol_info = pprSkolInfo skol_info
224 couldNotDeduce :: [EvVar] -> [PredType] -> SDoc
225 couldNotDeduce givens wanteds
226 = sep [ ptext (sLit "Could not deduce") <+> pprTheta wanteds
227 , nest 2 $ ptext (sLit "from the context")
228 <+> pprEvVarTheta givens]
230 getUserGivens :: ReportErrCtxt -> Maybe [EvVar]
231 -- Just gs => Say "could not deduce ... from gs"
232 -- Nothing => No interesting givens, say something else
233 getUserGivens (CEC {cec_encl = ctxt})
234 | null user_givens = Nothing
235 | otherwise = Just user_givens
237 givens = foldl (\gs ic -> ic_given ic ++ gs) [] ctxt
238 user_givens | opt_PprStyle_Debug = givens
239 | otherwise = filterOut isSelfDict givens
240 -- In user mode, don't show the "self-dict" given
241 -- which is only added to do co-inductive solving
242 -- Rather an awkward hack, but there we are
243 -- This is the only use of isSelfDict, so it's not in an inner loop
247 %************************************************************************
249 Implicit parameter errors
251 %************************************************************************
254 reportIPErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
255 reportIPErrs ctxt ips orig
256 = addErrorReport ctxt $ addArising orig msg
258 msg | Just givens <- getUserGivens ctxt
259 = couldNotDeduce givens ips
261 = sep [ ptext (sLit "Unbound implicit parameter") <> plural ips
262 , nest 2 (pprTheta ips) ]
266 %************************************************************************
270 %************************************************************************
273 reportEqErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
274 reportEqErrs ctxt eqs orig
275 = mapM_ report_one eqs
278 report_one (EqPred ty1 ty2)
279 = do { (env1, extra) <- getWantedEqExtra emptyTvSubst env0 orig ty1 ty2
280 ; let ctxt' = ctxt { cec_tidy = env1
281 , cec_extra = cec_extra ctxt $$ extra }
282 ; reportEqErr ctxt' ty1 ty2 }
284 = pprPanic "reportEqErrs" (ppr pred)
286 reportEqErr :: ReportErrCtxt -> TcType -> TcType -> TcM ()
287 reportEqErr ctxt ty1 ty2
288 | Just tv1 <- tcGetTyVar_maybe ty1 = reportTyVarEqErr ctxt tv1 ty2
289 | Just tv2 <- tcGetTyVar_maybe ty2 = reportTyVarEqErr ctxt tv2 ty1
290 | otherwise -- Neither side is a type variable
291 -- Since the unsolved constraint is canonical,
292 -- it must therefore be of form (F tys ~ ty)
293 = addErrorReport ctxt (msg $$ mkTyFunInfoMsg ty1 ty2)
295 msg = case getUserGivens ctxt of
296 Just givens -> couldNotDeduce givens [EqPred ty1 ty2]
297 Nothing -> misMatchMsg ty1 ty2
299 reportTyVarEqErr :: ReportErrCtxt -> TcTyVar -> TcType -> TcM ()
300 reportTyVarEqErr ctxt tv1 ty2
302 , Just tv2 <- tcGetTyVar_maybe ty2
304 = -- sk ~ alpha: swap
305 reportTyVarEqErr ctxt tv2 ty1
308 = -- sk ~ ty, where ty isn't a meta-tyvar: mis-match
309 addErrTcM (misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2)
311 -- So tv is a meta tyvar, and presumably it is
312 -- an *untouchable* meta tyvar, else it'd have been unified
313 | not (k2 `isSubKind` k1) -- Kind error
314 = addErrorReport ctxt $ (kindErrorMsg (mkTyVarTy tv1) ty2)
316 -- Check for skolem escape
317 | (implic:_) <- cec_encl ctxt -- Get the innermost context
318 , let esc_skols = varSetElems (tyVarsOfType ty2 `intersectVarSet` ic_skols implic)
319 implic_loc = ic_loc implic
320 , not (null esc_skols)
321 = setCtLoc implic_loc $ -- Override the error message location from the
322 -- place the equality arose to the implication site
323 do { (env1, env_sigs) <- findGlobals ctxt (unitVarSet tv1)
324 ; let msg = misMatchMsg ty1 ty2
325 esc_doc | isSingleton esc_skols
326 = ptext (sLit "because this skolem type variable would escape:")
328 = ptext (sLit "because these skolem type variables would escape:")
329 extra1 = vcat [ nest 2 $ esc_doc <+> pprQuotedList esc_skols
330 , sep [ (if isSingleton esc_skols
331 then ptext (sLit "This skolem is")
332 else ptext (sLit "These skolems are"))
333 <+> ptext (sLit "bound by")
334 , nest 2 $ pprSkolInfo (ctLocOrigin implic_loc) ] ]
335 ; addErrTcM (env1, msg $$ extra1 $$ mkEnvSigMsg (ppr tv1) env_sigs) }
337 -- Nastiest case: attempt to unify an untouchable variable
338 | (implic:_) <- cec_encl ctxt -- Get the innermost context
339 , let implic_loc = ic_loc implic
340 given = ic_given implic
341 = setCtLoc (ic_loc implic) $
342 do { let (env1, msg) = misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2
343 extra = vcat [ ptext (sLit "because") <+> ppr tv1 <+> ptext (sLit "is untouchable")
344 , ptext (sLit "inside the constraints") <+> pprEvVarTheta given
345 , nest 2 (ptext (sLit "bound at")
346 <+> pprSkolInfo (ctLocOrigin implic_loc)) ]
347 ; addErrTcM (env1, msg $$ extra) }
349 | otherwise -- I'm not sure how this can happen!
350 = addErrTcM (misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2)
352 is_meta1 = isMetaTyVar tv1
357 mkTyFunInfoMsg :: TcType -> TcType -> SDoc
358 -- See Note [Non-injective type functions]
359 mkTyFunInfoMsg ty1 ty2
360 | Just (tc1,_) <- tcSplitTyConApp_maybe ty1
361 , Just (tc2,_) <- tcSplitTyConApp_maybe ty2
362 , tc1 == tc2, isSynFamilyTyCon tc1
363 = ptext (sLit "NB:") <+> quotes (ppr tc1)
364 <+> ptext (sLit "is a type function") <> (pp_inj tc1)
367 pp_inj tc | isInjectiveTyCon tc = empty
368 | otherwise = ptext (sLit (", and may not be injective"))
370 misMatchMsgWithExtras :: TidyEnv -> TcType -> TcType -> (TidyEnv, SDoc)
371 -- This version is used by TcSimplify too, which doesn't track the
372 -- expected/acutal thing, so we just have ty1 ty2 here
373 -- NB: The types are already tidied
374 misMatchMsgWithExtras env ty1 ty2
375 = (env2, sep [ misMatchMsg ty1 ty2, nest 2 (extra1 $$ extra2) ])
377 (env1, extra1) = typeExtraInfoMsg env ty1
378 (env2, extra2) = typeExtraInfoMsg env1 ty2
380 misMatchMsg :: TcType -> TcType -> SDoc -- Types are already tidy
381 misMatchMsg ty1 ty2 = sep [ ptext (sLit "Couldn't match type") <+> quotes (ppr ty1)
382 , nest 15 $ ptext (sLit "with") <+> quotes (ppr ty2)]
384 kindErrorMsg :: TcType -> TcType -> SDoc -- Types are already tidy
386 = vcat [ ptext (sLit "Kind incompatibility when matching types:")
387 , nest 2 (vcat [ ppr ty1 <+> dcolon <+> ppr k1
388 , ppr ty2 <+> dcolon <+> ppr k2 ]) ]
393 typeExtraInfoMsg :: TidyEnv -> Type -> (TidyEnv, SDoc)
394 -- Shows a bit of extra info about skolem constants
395 typeExtraInfoMsg env ty
396 | Just tv <- tcGetTyVar_maybe ty
398 , isSkolemTyVar tv || isSigTyVar tv
400 , let (env1, tv1) = tidySkolemTyVar env tv
401 = (env1, pprSkolTvBinding tv1)
403 typeExtraInfoMsg env _ty = (env, empty) -- Normal case
406 unifyCtxt :: EqOrigin -> TidyEnv -> TcM (TidyEnv, SDoc)
407 unifyCtxt (UnifyOrigin { uo_actual = act_ty, uo_expected = exp_ty }) tidy_env
408 = do { act_ty' <- zonkTcType act_ty
409 ; exp_ty' <- zonkTcType exp_ty
410 ; let (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
411 (env2, act_ty'') = tidyOpenType env1 act_ty'
412 ; return (env2, mkExpectedActualMsg act_ty'' exp_ty'') }
414 mkExpectedActualMsg :: Type -> Type -> SDoc
415 mkExpectedActualMsg act_ty exp_ty
416 = vcat [ text "Expected type" <> colon <+> ppr exp_ty
417 , text " Actual type" <> colon <+> ppr act_ty ]
420 Note [Non-injective type functions]
421 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
422 It's very confusing to get a message like
423 Couldn't match expected type `Depend s'
424 against inferred type `Depend s1'
425 so mkTyFunInfoMsg adds:
426 NB: `Depend' is type function, and hence may not be injective
428 Warn of loopy local equalities that were dropped.
431 %************************************************************************
435 %************************************************************************
438 reportDictErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
439 reportDictErrs ctxt wanteds orig
440 = do { inst_envs <- tcGetInstEnvs
441 ; let (others, overlaps) = partitionWith (check_overlap inst_envs) wanteds
442 ; unless (null others) $
443 addErrorReport ctxt (mk_no_inst_err others)
444 ; mapM_ (addErrorReport ctxt) overlaps }
446 check_overlap :: (InstEnv,InstEnv) -> PredType -> Either PredType SDoc
447 -- Right msg => overlap message
448 -- Left inst => no instance
449 check_overlap inst_envs pred@(ClassP clas tys)
450 = case lookupInstEnv inst_envs clas tys of
451 ([], _) -> Left pred -- No match
452 -- The case of exactly one match and no unifiers means a
453 -- successful lookup. That can't happen here, because dicts
454 -- only end up here if they didn't match in Inst.lookupInst
456 | debugIsOn -> pprPanic "check_overlap" (ppr pred)
457 res -> Right (mk_overlap_msg pred res)
458 check_overlap _ _ = panic "check_overlap"
460 mk_overlap_msg pred (matches, unifiers)
461 = ASSERT( not (null matches) )
462 vcat [ addArising orig (ptext (sLit "Overlapping instances for")
464 , sep [ptext (sLit "Matching instances") <> colon,
465 nest 2 (vcat [pprInstances ispecs, pprInstances unifiers])]
466 , if not (isSingleton matches)
467 then -- Two or more matches
469 else -- One match, plus some unifiers
470 ASSERT( not (null unifiers) )
471 parens (vcat [ptext (sLit "The choice depends on the instantiation of") <+>
472 quotes (pprWithCommas ppr (varSetElems (tyVarsOfPred pred))),
473 ptext (sLit "To pick the first instance above, use -XIncoherentInstances"),
474 ptext (sLit "when compiling the other instance declarations")])]
476 ispecs = [ispec | (ispec, _) <- matches]
478 mk_no_inst_err :: [PredType] -> SDoc
479 mk_no_inst_err wanteds
480 | Just givens <- getUserGivens ctxt
481 = vcat [ addArising orig $ couldNotDeduce givens wanteds
482 , show_fixes (fix1 : fixes2) ]
484 | otherwise -- Top level
485 = vcat [ addArising orig $
486 ptext (sLit "No instance") <> plural wanteds
487 <+> ptext (sLit "for") <+> pprTheta wanteds
488 , show_fixes fixes2 ]
491 fix1 = sep [ ptext (sLit "add") <+> pprTheta wanteds
492 <+> ptext (sLit "to the context of")
493 , nest 2 $ pprErrCtxtLoc ctxt ]
495 fixes2 | null instance_dicts = []
496 | otherwise = [sep [ptext (sLit "add an instance declaration for"),
497 pprTheta instance_dicts]]
498 instance_dicts = filterOut isTyVarClassPred wanteds
499 -- Insts for which it is worth suggesting an adding an
500 -- instance declaration. Exclude tyvar dicts.
502 show_fixes :: [SDoc] -> SDoc
503 show_fixes [] = empty
504 show_fixes (f:fs) = sep [ptext (sLit "Possible fix:"),
505 nest 2 (vcat (f : map (ptext (sLit "or") <+>) fs))]
507 reportAmbigErrs :: ReportErrCtxt -> TcTyVarSet -> [WantedEvVar] -> TcM ()
508 reportAmbigErrs ctxt skols ambigs
509 -- Divide into groups that share a common set of ambiguous tyvars
510 = mapM_ report (equivClasses cmp ambigs_w_tvs)
512 ambigs_w_tvs = [ (d, varSetElems (tyVarsOfWantedEvVar d `minusVarSet` skols))
514 cmp (_,tvs1) (_,tvs2) = tvs1 `compare` tvs2
516 report :: [(WantedEvVar, [TcTyVar])] -> TcM ()
519 do { let main_msg = sep [ text "Ambiguous type variable" <> plural tvs
520 <+> pprQuotedList tvs
521 <+> text "in the constraint" <> plural pairs <> colon
522 , nest 2 pp_wanteds ]
523 ; (tidy_env, mono_msg) <- mkMonomorphismMsg ctxt tvs
524 ; addErrTcM (tidy_env, main_msg $$ mono_msg) }
527 (loc, pp_wanteds) = pprWithArising (map fst pairs)
529 mkMonomorphismMsg :: ReportErrCtxt -> [TcTyVar] -> TcM (TidyEnv, SDoc)
530 -- There's an error with these Insts; if they have free type variables
531 -- it's probably caused by the monomorphism restriction.
532 -- Try to identify the offending variable
533 -- ASSUMPTION: the Insts are fully zonked
534 mkMonomorphismMsg ctxt inst_tvs
535 = do { dflags <- getDOpts
536 ; traceTc "Mono" (vcat (map pprSkolTvBinding inst_tvs))
537 ; (tidy_env, docs) <- findGlobals ctxt (mkVarSet inst_tvs)
538 ; return (tidy_env, mk_msg dflags docs) }
540 mk_msg _ _ | any isRuntimeUnkSkol inst_tvs -- See Note [Runtime skolems]
541 = vcat [ptext (sLit "Cannot resolve unknown runtime types:") <+>
542 (pprWithCommas ppr inst_tvs),
543 ptext (sLit "Use :print or :force to determine these types")]
544 mk_msg _ [] = ptext (sLit "Probable fix: add a type signature that fixes these type variable(s)")
545 -- This happens in things like
546 -- f x = show (read "foo")
547 -- where monomorphism doesn't play any role
549 = vcat [ptext (sLit "Possible cause: the monomorphism restriction applied to the following:"),
551 monomorphism_fix dflags]
553 monomorphism_fix :: DynFlags -> SDoc
554 monomorphism_fix dflags
555 = ptext (sLit "Probable fix:") <+> vcat
556 [ptext (sLit "give these definition(s) an explicit type signature"),
557 if xopt Opt_MonomorphismRestriction dflags
558 then ptext (sLit "or use -XNoMonomorphismRestriction")
559 else empty] -- Only suggest adding "-XNoMonomorphismRestriction"
560 -- if it is not already set!
563 -----------------------
564 -- findGlobals looks at the value environment and finds values whose
565 -- types mention any of the offending type variables. It has to be
566 -- careful to zonk the Id's type first, so it has to be in the monad.
567 -- We must be careful to pass it a zonked type variable, too.
569 mkEnvSigMsg :: SDoc -> [SDoc] -> SDoc
570 mkEnvSigMsg what env_sigs
571 | null env_sigs = empty
572 | otherwise = vcat [ ptext (sLit "The following variables have types that mention") <+> what
573 , nest 2 (vcat env_sigs) ]
575 findGlobals :: ReportErrCtxt
577 -> TcM (TidyEnv, [SDoc])
580 = do { lcl_ty_env <- case cec_encl ctxt of
582 (i:_) -> return (ic_env i)
583 ; go (cec_tidy ctxt) [] (nameEnvElts lcl_ty_env) }
585 go tidy_env acc [] = return (tidy_env, acc)
586 go tidy_env acc (thing : things) = do
587 (tidy_env1, maybe_doc) <- find_thing tidy_env ignore_it thing
589 Just d -> go tidy_env1 (d:acc) things
590 Nothing -> go tidy_env1 acc things
592 ignore_it ty = tvs `disjointVarSet` tyVarsOfType ty
594 -----------------------
595 find_thing :: TidyEnv -> (TcType -> Bool)
596 -> TcTyThing -> TcM (TidyEnv, Maybe SDoc)
597 find_thing tidy_env ignore_it (ATcId { tct_id = id })
598 = do { id_ty <- zonkTcType (idType id)
599 ; if ignore_it id_ty then
600 return (tidy_env, Nothing)
602 { let (tidy_env', tidy_ty) = tidyOpenType tidy_env id_ty
603 msg = sep [ ppr id <+> dcolon <+> ppr tidy_ty
604 , nest 2 (parens (ptext (sLit "bound at") <+>
605 ppr (getSrcLoc id)))]
606 ; return (tidy_env', Just msg) } }
608 find_thing tidy_env ignore_it (ATyVar tv ty)
609 = do { tv_ty <- zonkTcType ty
610 ; if ignore_it tv_ty then
611 return (tidy_env, Nothing)
613 { let -- The name tv is scoped, so we don't need to tidy it
614 (tidy_env1, tidy_ty) = tidyOpenType tidy_env tv_ty
615 msg = sep [ ptext (sLit "Scoped type variable") <+> quotes (ppr tv) <+> eq_stuff
618 eq_stuff | Just tv' <- tcGetTyVar_maybe tv_ty
619 , getOccName tv == getOccName tv' = empty
620 | otherwise = equals <+> ppr tidy_ty
621 -- It's ok to use Type.getTyVar_maybe because ty is zonked by now
622 bound_at = parens $ ptext (sLit "bound at:") <+> ppr (getSrcLoc tv)
624 ; return (tidy_env1, Just msg) } }
626 find_thing _ _ thing = pprPanic "find_thing" (ppr thing)
628 warnDefaulting :: [WantedEvVar] -> Type -> TcM ()
629 warnDefaulting wanteds default_ty
630 = do { warn_default <- doptM Opt_WarnTypeDefaults
631 ; setCtLoc loc $ warnTc warn_default warn_msg }
634 warn_msg = vcat [ ptext (sLit "Defaulting the following constraint(s) to type") <+>
635 quotes (ppr default_ty),
637 (loc, ppr_wanteds) = pprWithArising wanteds
640 Note [Runtime skolems]
641 ~~~~~~~~~~~~~~~~~~~~~~
642 We want to give a reasonably helpful error message for ambiguity
643 arising from *runtime* skolems in the debugger. These
644 are created by in RtClosureInspect.zonkRTTIType.
647 %************************************************************************
649 Error from the canonicaliser
650 These ones are called *during* constraint simplification
652 %************************************************************************
655 kindErrorTcS :: CtFlavor -> TcType -> TcType -> TcS a
656 -- If there's a kind error, we don't want to blindly say "kind error"
657 -- We might, say, be unifying a skolem 'a' with a type 'Int',
658 -- in which case that's the error to report. So we set things
659 -- up to call reportEqErr, which does the business properly
660 kindErrorTcS fl ty1 ty2
661 = wrapEqErrTcS fl ty1 ty2 $ \ env0 ty1 ty2 extra ->
662 do { let ctxt = CEC { cec_encl = []
665 ; reportEqErr ctxt ty1 ty2
669 misMatchErrorTcS :: CtFlavor -> TcType -> TcType -> TcS a
670 misMatchErrorTcS fl ty1 ty2
671 = wrapEqErrTcS fl ty1 ty2 $ \ env0 ty1 ty2 extra ->
672 do { let (env1, msg) = misMatchMsgWithExtras env0 ty1 ty2
673 ; failWithTcM (env1, inaccessible_msg $$ msg $$ extra) }
677 Given loc -> hang (ptext (sLit "Inaccessible code in"))
681 = case ctLocOrigin loc of
682 PatSkol dc mc -> sep [ ptext (sLit "a pattern with constructor")
683 <+> quotes (ppr dc) <> comma
684 , ptext (sLit "in") <+> pprMatchContext mc ]
685 other_skol -> pprSkolInfo other_skol
687 occursCheckErrorTcS :: CtFlavor -> TcTyVar -> TcType -> TcS a
688 occursCheckErrorTcS fl tv ty
689 = wrapEqErrTcS fl (mkTyVarTy tv) ty $ \ env0 ty1 ty2 extra2 ->
690 do { let extra1 = sep [ppr ty1, char '=', ppr ty2]
691 ; failWithTcM (env0, hang msg 2 (extra1 $$ extra2)) }
693 msg = text $ "Occurs check: cannot construct the infinite type:"
695 solverDepthErrorTcS :: Int -> [CanonicalCt] -> TcS a
696 solverDepthErrorTcS depth stack
697 | null stack -- Shouldn't happen unless you say -fcontext-stack=0
698 = wrapErrTcS $ failWith msg
701 setCtFlavorLoc (cc_flavor top_item) $
702 do { env0 <- tcInitTidyEnv
703 ; let ev_vars = map cc_id stack
704 env1 = tidyFreeTyVars env0 free_tvs
705 free_tvs = foldr (unionVarSet . tyVarsOfEvVar) emptyVarSet ev_vars
706 extra = pprEvVars (map (tidyEvVar env1) ev_vars)
707 ; failWithTcM (env1, hang msg 2 extra) }
709 top_item = head stack
710 msg = vcat [ ptext (sLit "Context reduction stack overflow; size =") <+> int depth
711 , ptext (sLit "Use -fcontext-stack=N to increase stack size to N") ]
713 flattenForAllErrorTcS :: CtFlavor -> TcType -> Bag CanonicalCt -> TcS a
714 flattenForAllErrorTcS fl ty _bad_eqs
717 do { env0 <- tcInitTidyEnv
718 ; let (env1, ty') = tidyOpenType env0 ty
719 msg = sep [ ptext (sLit "Cannot deal with a type function under a forall type:")
721 ; failWithTcM (env1, msg) }
724 %************************************************************************
728 %************************************************************************
731 setCtFlavorLoc :: CtFlavor -> TcM a -> TcM a
732 setCtFlavorLoc (Wanted loc) thing = setCtLoc loc thing
733 setCtFlavorLoc (Derived loc _) thing = setCtLoc loc thing
734 setCtFlavorLoc (Given loc) thing = setCtLoc loc thing
736 wrapEqErrTcS :: CtFlavor -> TcType -> TcType
737 -> (TidyEnv -> TcType -> TcType -> SDoc -> TcM a)
739 wrapEqErrTcS fl ty1 ty2 thing_inside
740 = do { ty_binds_var <- getTcSTyBinds
741 ; wrapErrTcS $ setCtFlavorLoc fl $
742 do { -- Apply the current substitition
743 -- and zonk to get rid of flatten-skolems
744 ; ty_binds_map <- readTcRef ty_binds_var
745 ; let subst = mkOpenTvSubst (mapVarEnv snd ty_binds_map)
746 ; env0 <- tcInitTidyEnv
747 ; (env1, ty1) <- zonkSubstTidy env0 subst ty1
748 ; (env2, ty2) <- zonkSubstTidy env1 subst ty2
749 ; let do_wanted loc = do { (env3, extra) <- getWantedEqExtra subst env2
750 (ctLocOrigin loc) ty1 ty2
751 ; thing_inside env3 ty1 ty2 extra }
753 Wanted loc -> do_wanted loc
754 Derived loc _ -> do_wanted loc
755 Given {} -> thing_inside env2 ty1 ty2 empty
756 -- We could print more info, but it
757 -- seems to be coming out already
761 getWantedEqExtra :: TvSubst -> TidyEnv -> CtOrigin -> TcType -> TcType
762 -> TcM (TidyEnv, SDoc)
763 getWantedEqExtra subst env0 (TypeEqOrigin item) ty1 ty2
764 -- If the types in the error message are the same
765 -- as the types we are unifying (remember to zonk the latter)
766 -- don't add the extra expected/actual message
768 -- The complication is that the types in the TypeEqOrigin must
770 -- (b) have any TcS-monad pending equalities applied to them
771 -- (hence the passed-in substitution)
772 = do { (env1, act) <- zonkSubstTidy env0 subst (uo_actual item)
773 ; (env2, exp) <- zonkSubstTidy env1 subst (uo_expected item)
774 ; if (act `tcEqType` ty1 && exp `tcEqType` ty2)
775 || (exp `tcEqType` ty1 && act `tcEqType` ty2)
779 return (env2, mkExpectedActualMsg act exp) }
781 getWantedEqExtra _ env0 orig _ _
782 = return (env0, pprArising orig)
784 zonkSubstTidy :: TidyEnv -> TvSubst -> TcType -> TcM (TidyEnv, TcType)
785 -- In general, becore printing a type, we want to
786 -- a) Zonk it. Even during constraint simplification this is
787 -- is important, to un-flatten the flatten skolems in a type
788 -- b) Substitute any solved unification variables. This is
789 -- only important *during* solving, becuase after solving
790 -- the substitution is expressed in the mutable type variables
791 -- But during solving there may be constraint (F xi ~ ty)
792 -- where the substitution has not been applied to the RHS
793 zonkSubstTidy env subst ty
794 = do { ty' <- zonkTcTypeAndSubst subst ty
795 ; return (tidyOpenType env ty') }